生物载体与曝气方式对氧化池氧转移特性的影响

对比研究了不同曝气量条件下,分别采用穿孔曝气和微孔曝气时,装填不同载体的接触氧化池的氧转移特性。结果表明,在试验范围内,各接触氧化池的氧总传质系数均随曝气量的增加而增大,但增加速度逐渐变缓。当曝气量为3.5 m3/h时,网格载体池的氧转移效率和动力效率达到最大值,分别为5.25%和3.22 kgO2/(kW.h),是竖管载体池和悬浮球载体池的1.14倍,是无载体池的1.22倍。当处理对象为生活污水时,接触氧化池内可采用微孔曝气+竖管(或悬浮球)载体;而当处理对象为高浓度有机废水时,可采用穿孔曝气+网格载体+悬浮球载体。     

Promotion and inhibition of oxygen transfer under fine bubble aeration by activated sludge

The promotion and inhibition of inactivated and activated sludge on oxygen mass transfer (OMT) were studied using lab‐scale experiments. The results showed that the α‐values and oxygen transfer efficiency (OTE) decreased with increasing mixed liquor suspended solids (MLSS) concentration (1–10 g/L). Although OMT promotion rate by microbial respiration in activated sludge system increased from 39.8–97.5% for the α‐values and OTE, the two parameters were found to fall sharply when MLSS concentration was over 5 g/L. This indicated that the sludge concentration is a major influence factor on OMT in activated sludge system. Such results provide valuable knowledge for the operating optimization of the aeration system in wastewater treatment process.     

中空纤维膜无泡曝气氧传质性能试验研究

为探究中空纤维膜无泡曝气技术水体充氧性能,使用聚四氟乙烯(PTFE)和聚丙烯(PP)两种材质的中空纤维膜组件,分别在曝气压强为2、4、6 kPa,曝气流量为18、36、54 L/h条件下进行清水曝气测试,并对两种中空纤维膜的氧传质系数、氧传质速率以及曝气效率等进行分析。结果表明,PTFE和PP两种中空纤维膜组件均能实现无泡曝气,且PP中空纤维膜组件的充氧效果相比PTFE组件要好;当曝气压强为4 kPa、曝气流量为36 L/h时,PTFE和PP膜组件的氧传质速率分别为0.326、0.550 g/(m^2·h)。中空纤维膜无泡曝气技术具有操作压力小、氧传质速率高等特点,充氧效果优于传统曝气。     

A study of optimum aeration efficiency of a lab‐scale air‐diffused system

Up to now, tremendous efforts have been devoted to modelling the oxygen transfer coefficient (k_La) for diffused aeration systems, while not considering the corresponding energy consumption. Enhancing k_La is favorable for an exemplary oxygenation process, but may come at the cost of greater energy withdrawal, an unwelcome tradeoff. Assessing the aeration efficiency (the rate of oxygen delivered per unit energy) reflects the overall effectiveness of an aeration process and guarantees a superior system performance. Presented here is a lab‐scale study that investigates the effect of the orifice diameter, the airflow rate and the water column on the aeration efficiency. Various combinations of the studied parameters were tested using a cylindrical tank with a single orifice for air injection. An optimal performance of the aeration efficiency was observed at an orifice diameter of 0.3 mm when tested under 0.91 m water column and an airflow rate of 0.05 SLPM. Furthermore, a new empirical formula of aeration efficiency was established with a high correlation index (R² = 0.97) to allow preliminary prediction of aeration efficiency.     

An experimental investigation of aeration performance in stepped spillways

Dissolved oxygen content is a prime indicator of water quality. The oxygen transfer across the air–water interface at a hydraulic structure, such as a weir or spillway, occurs by self‐aeration along the chute and by flow aeration in the hydraulic jump at the downstream end of the structure. Despite increased research activities in the field of stepped spillways, the aeration efficiency of stepped spillways is not yet known. This paper investigates the aeration efficiency of stepped spillways, in particular the effects of varying chute angle and step height. Empirical correlations predicting length of the nonaerated flow region and aeration efficiency were developed. The results indicate that stepped spillways are effective for oxygen transfer.     

Factors influencing oxygen transfer in fine pore diffused aeration

A bench-scale experiment was conducted in a 701. tank of tap water to examine the effect of four design variables on oxygen transfer in a fine pore diffused aeration system. The experiment used non-steady state gas transfer methodology to examine the effect of air flow rate, air flow rate per diffuser, orifice diameter and reduced tank surface area on the overall oxygen transfer coefficient (K_La₂₀, h⁻¹); standard oxygen transfer rate (OT₂, g O₂ h⁻¹); energy efficiency (E_p, g O₂ kWh⁻¹) and oxygen transfer efficiency (E_o, %). The experiments demonstrated that K_La₂₀ and OT_s increased with air flow rate (9.4–18.8 1 min⁻¹) in the 40 and 140 μ diameter orifice range; however, E_p and E₀ were not affected. Reducing the air flow rate per fine pore diffuser (40 and 140 μ diameter pore size) significantly increased K_La₂₀, OT_s, E_p and E₀. A decrease in orifice diameter from 140 to 40 μ had no effect on K_La₂₀, OT_s, E_p and E₀. A reduction in tank surface area had a marginally significant inverse effect on K_La₂₀ and OT_s, and no effect on E_p and E_o. The mean bubble size produced by the 40 and 140 μ diffusers was 4.0 and 4.2 mm, respectively. There was no consistent effect of air flow rate on bubble size within the range of air flow rates used in this experiment. In clean water aeration applications, the optimum system efficiency will be obtained using the largest number of fine pore diffusers operated at low air flow rates per diffuser. In wastewater treatment plants, higher air flow rates per diffuser should be used to prevent diffuser biofouling and keep biological solids in suspension. Wastewater systems are purposely operated at less than optimum transfer efficiencies in exchange for reduced diffuser maintenance and improved mixing. In either situation, changes in tank surface area and diffuser pore size (provided that pore diameter remains between 40 and 140 μ) are unlikely to have any significant effect on aeration system efficiency.     

有机碳源及溶解氧对污水脱氮除磷的影响

介绍了有机碳源、溶解氧对常用污水生物脱氮处理工艺（A2O,Carrousel氧化沟,SBR）的影响,指出反硝化除磷、间歇曝气、低氧脱氮除磷技术在处理低碳、高氮磷城市污水方面具有良好的发展前景。     

Hypolimnetic aeration: practical design and application

Hypolimnetic aeration is becoming increasingly important as a fisheries management and water quality improvement technique, however its application has been restricted by a paucity of practical reference material. Hypolimnetic aeration includes partial and full lift designs and several air/oxygen injection systems. Positive displacement compressors flanged to three phase electric motors are the preferred air supply and power for most lake aeration projects. Internal combustion power is adequate for short term use and wind power is in the developmental stage. Rubber compressed air hose is recommended for lake aeration applications. Free air delivery is the air volume taken into the compressor at standard temperature and pressure however actual output volume is regulated by discharge pressure. Performance specifications of full lift hypolimnetic aerators are based on water:air ratios, oxygen increase, transfer efficiencies and oxygenation capacity. An empirical sizing method is proposed using hypolimnetic volume, hypolimnetic oxygen consumption, water flow, air flow and inflow tube radius. Outflow tube radius should equal or exceed inflow tube radius to achieve high flow rates and allow efficient removal of residual bubbles. Floatation requirements are calculated from the total weight of the separator box, inflow and outflow tubes and the theoretical water head.     

Membrane properties change in fine-pore aeration diffusers: full-scale variations of transfer efficiency and headloss

Fine-pore diffusers are the most common aeration system in municipal wastewater treatment. Punched polymeric membranes are often used in fine-pore aeration due to their advantageous initial performance. These membranes are subject to fouling and scaling, resulting in increased headloss and reduced oxygen transfer efficiency, both contributing to increased plant energy costs. This paper describes and discusses the change in material properties for polymeric fine-pore diffusers, comparing new and used membranes. Three different diffuser technologies were tested and sample diffusers from two wastewater treatment facilities were analysed. The polymeric membranes analysed in this paper were composed of ethylene-propylene-diene monomer (EPDM), polyurethane, and silicon. Transfer efficiency is usually lower with longer times in operation, as older, dilated orifices produce larger bubbles, which are unfavourable to mass transfer. At the same time, headloss increases with time in operation, since membranes increase in rigidity and hardness, and fouling and scaling phenomena occur at the orifice opening. Change in polymer properties and laboratory test results correlate with the decrease in oxygen transfer efficiency.     

兴平市污水处理厂VT深井曝气工艺的设计与运行

陕西省兴平市城市污水处理厂在国内首次引进加拿大VERTREATTM(简称VT)深井曝气工艺。该厂规模为5×104m3/d,出水执行《城镇污水处理厂污染物排放标准》(GB 18918—2002)的二级标准,实际出水水质达到一级B标准。VT工艺的主体反应器由两口直径为3.2 m、深为92 m的深井组成。整个VT生化系统的占地面积为4 400 m2。深井反应器内的氧气利用率为65%～86%,并实现"一气多用":曝气除满足微生物新陈代谢需要外,还用于混合液搅拌、气提、后续气浮泥水分离等,大大节省了运行成本,处理电耗约0.8 kW.h/kgBOD5。     

Water surface contacting cover system--the basic study for improving the oxygen transfer coefficient and the BOD removal capacity

In order to construct an environmental aeration basin in a sewage treatment plant, the suggested novel aeration basin was examined for the oxygen transfer coefficient by using tap water on a lab-scale and pilot-scale. We called it water surface contacting cover system (WSCCS) that was installed with a cover plate on the wafer surface and a slant plate in aeration basin, compared to a standard aeration basin (SRAS, spiral roll aeration system). Finally, the novel basin could be compared by adopting the slant and cover plates into the actual sewage treatment plant (W x L x D (m)=5.0 x 2.65 x 4.25, treatment capacity: 600 m3/d). As a result, only by adding a slant plate, the oxygen transfer coefficient (K(L)a) increased approximately by 15% more than that with a SRAS basin. And the slope of slant plate was optimized at 10 degrees . Additionally, in the WSCCS, the increasing efficiency of the oxygen transfer coefficient, affected only by the cover, was proved at about 25% on the lab-scale aeration basin and about 20% on the pilot plant. After all, the increasing effect of the oxygen transfer coefficient on WSCCS that was installed with the water contacting cover and the slant plate on standard aeration basin was proved to be above 35%. The distance between the air diffuser and the slant plate was 20-30 cm in the pilot-scale plant. As an effective factor for increasing the oxygen transfer rate, the width/depth ratio of aeration basin was proved to be 2. Through the short-term results of actual sewage treatment plant, it was known that BOD removal efficiency could be improved by about 3% by adopting tile WSCCS not but SRAS.     

水质对中空纤维膜曝气效果的影响研究

通过间歇试验考察了水质对中空纤维膜曝气效果的影响。结果表明,随着水中有机物和其他杂质的增加,膜曝气的氧总传质系数（KLa）和饱和溶解氧（cs）的浓度不断下降,Kh由清水时的0．01853min^-1降到COD含量为900mg／L时的0．0126min^-1;cs值由12．54mg／L下降为10．04mg／L。对于池塘水,其KLa和cs下降幅度超过同等COD浓度的人工配水,这可能与池塘水质的复杂性有关。     

Hydrodynamic parameters of diffused air systems

The influence of hydrodynamic parameters of diffused air systems on the oxygen transfer efficiency and the longitudinal dispersion of liquid in diffused air aeration wastewater treatment tanks have been evaluated using dimensional analysis, which involved the identification of significant parameters, development of equations to relate the dimensionless mass transfer and dispersion criteria with dimensionless hydrodynamic and geometric variables, and experimentation to determine the necessary numerical values for these equations. The developed relationships can be used as a guide for the design and optimization of aeration tanks.     

Energy saving in activated sludge plants by the use of more efficient fine bubble diffusers

Many activated sludge plants (ASP) use fine bubble diffused air as their source of oxygen. Blowers are attached to air pipework, which distributes air to a network of diffusers installed on the floor of the ASP tank. Modern diffusers are made from a rubber membrane which flexes to allow fine bubbles of air to pass through holes in the diffusers which then pass into the mixed liquors in the tank. The diffusers come as circular discs, tubes and more recently mats or panels. Yorkshire Water is in the process of building new ASP at some of their biggest sewage treatment works to meet new final effluent consent standards associated with the freshwater fisheries directive (FFD). These new works will treat sewage from a combined population of over two million people in the Yorkshire area. Black & Veatch is involved in some of the first works to have a new type of fine bubble diffuser installed in the ASP basins. These diffusers resemble a mat or panel and are fixed to the floor of the tank as opposed to circular and tubular diffusers which as fixed above the floor. Oxygen transfer testing has been carried out to show the efficiency of these aeration systems, which may offer significant savings in operating costs to water operators. This paper examines the results from the tests and compares them with other tests carried out in the United States and tests that have been carried out on other types of diffusers. The paper will discuss the results of the oxygen transfer tests and present capital and net present costs (NPC) for various diffuser installations.     

Oxygen transfer and uptake, nutrient removal, and energy footprint of parallel full-scale IFAS and activated sludge processes

Integrated fixed-film activated sludge (IFAS) processes are becoming more popular for both secondary and sidestream treatment in wastewater facilities. These processes are a combination of biofilm reactors and activated sludge processes, achieved by introducing and retaining biofilm carrier media in activated sludge reactors. A full-scale train of three IFAS reactors equipped with AnoxKaldnes media and coarse-bubble aeration was tested using off-gas analysis. This was operated independently in parallel to an existing full-scale activated sludge process. Both processes achieved the same percent removal of COD and ammonia, despite the double oxygen demand on the IFAS reactors. In order to prevent kinetic limitations associated with DO diffusional gradients through the IFAS biofilm, this systems was operated at an elevated dissolved oxygen concentration, in line with the manufacturer’s recommendation. Also, to avoid media coalescence on the reactor surface and promote biofilm contact with the substrate, high mixing requirements are specified. Therefore, the air flux in the IFAS reactors was much higher than that of the parallel activated sludge reactors. However, the standardized oxygen transfer efficiency in process water was almost same for both processes. In theory, when the oxygen transfer efficiency is the same, the air used per unit load removed should be the same. However, due to the high DO and mixing requirements, the IFAS reactors were characterized by elevated air flux and air use per unit load treated. This directly reflected in the relative energy footprint for aeration, which in this case was much higher for the IFAS system than activated sludge.     

Influence of mixed liquor recycle ratio and dissolved oxygen on performance of pre-denitrification submerged membrane bioreactors

The conflicting influence of mixed liquor recycle ratio and dissolved oxygen on nitrogen removal and membrane fouling of a pre-denitrification submerged MBR was investigated in this study. It was found that a high aeration rate of 10 L air/min was able to minimize membrane fouling as compared with lower aeration rates of 5 and 2.5L air/min in this study. Faster fouling at lower aeration rate was due to the decrease in cross-flow velocity across the membrane surface. However, high DO concentration (average of 5.1+/-0.5mg O2/L) present in the recycle mixed liquor at an aeration rate of 10 L air/min deteriorated the TN removal efficiency when operating at a recycle ratio of more than 3. A lower aeration rate of 5L air/min, resulting in an average DO concentration of 3.4+/-0.7 mg O2/L in the recycle mixed liquor, led to an improvement in TN removal efficiency: 63%, 80%, 84% and 89% for mixed liquor recycle ratio of 1, 3, 5 and 10, respectively. Further decrease in aeration rate to 2.5L air/min, resulting in an average DO concentration of 1.9+/-0.8 mg O2/L, did not improve the TN removal efficiency. Using a newly developed simplified nitrification-denitrification model, it was calculated that the COD/NO3(-)-N required for denitrification at 10 L air/min aeration rate was higher than those associated with 5 and 2.5L air/min aeration rates. The model also revealed that denitrification at an aeration rate of 10 L air/min was limited by COD concentration present in the wastewater when operating at a mixed liquor recycle ratio of 3 and higher.     

Aeration Performance of Triangular-Notch Weirs

Hydraulic structures have an impact on the concentration of dissolved oxygen in a river system, even though the water is in contact with the structure for only a short period of time. The same oxygen transfer that would normally occur over several kilometres in a river can occur at a single hydraulic structure, because the flow over a structure is typically highly turbulent, resulting in increased interfacial renewal. Plunging overfall jets from weirs are a good example of this fact, and the aeration properties of such structures have been studied widely in the laboratory and field over a number of years. This technical note (a) describes triangular-notch weirs having a different weir angle α and how they affect aeration performance, and (b) demonstrates that aeration efficiency decreases with increasing weir angle.     

喷射式内循环反应器处理生活污水中试

喷射式内循环生物反应器结合了射流曝气和环流反应器的特点，具有很高的氧传递效率，是一种高效的污水好氧生物处理技术：利用该技术处理生活污水的中试结果表明，反应器启动迅速，当水力停留时间为0．5～2h时对COD的去除率〉80％，对BOD5的去除率〉85％，出水氨氮达标排放。     

Experimental studies on air entrainment and oxygen content downstream of sharp-crested weirs

The concentration of dissolved oxygen (DO) is an important indicator of water quality because aquatic life survives on the DO in water. A free overfall jet from a weir plunging into downstream water causes entrainment of air bubbles if the free overfall jet velocity exceeds a certain critical value and hence aeration occurs. This paper investigates the free overfall jets from sharp‐crested weirs and their effect on air entrainment and aeration efficiency. The results indicate that the air entrainment and aeration efficiency of triangular sharp‐crested weirs are significantly better than those for the other sharp‐crested weir types. Therefore, the triangular sharp‐crested weirs can be used as highly effective aerators in streams, rivers, constructed channels, fish hatcheries, water treatment plants, etc. Regression equations were obtained for the triangular sharp‐crested weirs relating air entrainment rate and aeration efficiency to drop height, discharge and angle in the triangular sharp‐crested weir. There was good agreement between the measured values and the values computed from the predictive equations.     

榨菜综合废水好氧生物处理工艺的选择试验

针对榨菜综合废水呈高盐、高氮磷、高有机物浓度的水质特征,对两级SBR与单级SBBR反应器处理榨菜废水的效能进行了研究.结果表明:在温度为20℃、有机负荷为1.0 kg-COD/(m3·d)、DO为5 ms/L、反应器运行工况为进水(0.25 h)/曝气(11 h)/沉淀(0.5 h)/排水(0.25 h)的条件下,SBBR反应器能够使榨菜综合废水达标排放,而两级SBR工艺则不适宜处理榨菜综合废水.